The invention relates to an apparatus for optical measurement of an object, especially for measuring movement.
Accordingly, the apparatus comprises an interferometer for measuring movements along the axis of the measurement beam of the interferometer and a microscope with an objective and a focusing device, wherein the focusing device is embodied such that it can change the relative position of the object and the focal point of the objective relative to each other, wherein the interferometer and the microscope are allocated relative to each other, such that the measurement beam of the interferometer is projected onto the object over the beam path of the microscope.
The interferometer enables the measurement of movements along the axis of the measurement beam, that is, in general, movements perpendicular to the object plane of the microscope. In general, a laser Doppler vibrometer is used, for which a measurement point is illuminated on the object with coherent laser light. The movement of the surface of the object results in a Doppler shift of the frequency of the light reflected at the surface. An evaluation of this frequency shift or an equivalent phase shift by means of a demodulator enables the determination of the speed of the movement of the object surface at the measurement point. From the profile of this speed, the acceleration rate of the object surface at the measurement point can also be calculated. The principle design of such a measurement apparatus is described, for example, in the DE technical journal “Technisches Messen [Technical Measurement]—tm” 57 (1990), pages 335 to 345.
For measuring the movements of small objects, especially the movements or vibrations of miniaturized components in microsystem technology, frequently interferometers are used, whose measurement beam is projected over the beam path of a microscope onto the object to be measured.
The measurement beam of the interferometer can be aligned by means of the microscope on a defined measurement point on the object, wherein preferably the measurement point to be measured on the object comes to lie approximately at the focal point of the microscope, so that the measurement beam at the measurement point has the smallest extent possible and thus the smallest area possible is illuminated on the object, so that high local resolution is possible.
U.S. Pat. No. 6,084,672 discloses an apparatus for optical measurement of an object, especially for path and/or vibration measurement. The measurement is performed by means of a laser interferometer, wherein its measurement beam is coupled into the beam path of a microscope. The measurement beam reflected by the object is, in turn, decoupled from the beam path of the microscope and returned into the measurement system. Furthermore, the apparatus comprises a device for approximately parallel shifting of the measurement beam, so that multiple successive points can be measured on the object, without moving the measurement object.